This invention relates to an automatic transmission suitable for bicycles.
The vast majority of commercially available multi-speed bicycles are equipped with a chain-driven transmission of the type generically referred to as "derailleurs".
Although bicycles equipped with derailleur-type transmissions dominate the commercial market, they have many functional and operational problems which detract from their popularity. More specifically, derailleurs are made of a large number of exposed, delicate parts, which require frequent maintenance and adjustment. In addition, derailleur transmissions are hard to operate, since the operator must cognitively decide whether to actuate one or both derailleurs, to produce the desired gear change. Also derailleurs are typically noisy and prone to inefficiency due to chain misalignment and/or riders failure to completely derail the chain between sprocket rings. Furthermore, front derailleur systems can not be shifted smoothly while the chain is under load which, in turn, limits the capacity of the bicyclist to go smoothly, through the terrain encountered, which required the gear change. Finally, it is difficult to remove and reassemble the rear wheel of a multi-speed bicycle equipped with derailleur-type transmission.
In an effort to overcome the above-noted and other shortcomings associated with derailleur equipped bicycles, a plethora of alternative variable ratio transmissions have been proposed. Usually, such alternative transmissions are of the type generically referred to as "variable sprocket" transmissions, in which the effective diameter of a segmented front sprocket is selectively varied with respect to a constant diameter rear driven sprocket, for establishing different speed ratios between them.
From a pure engineering standpoint, such variable sprocket transmissions are superior to derailleur-type transmissions, since they can change speed under power in a very smooth manner. Also, different speed ratios are evenly sequenced for ease of operation. However, variable sprocket transmissions also have their shortcomings.
Although variable sprocket transmissions have been known for more than 20 years, they have not gained commercial acceptance. This is mainly due to their complexity and vast number of parts, which add to the cost of production, weight of the bicycle and susceptibility to mechanical failure. Furthermore in most cases in the above group, the variable diameter pulleys are applied only to the pedal crank, which results in a very limited gear ratio range.
In view of the above, there is a need to develop an automatic transmission for multi-speed bicycles which overcomes the deficiencies known in the prior art. It should be relatively simple in structure, compact and reliable in operation.
A patent search by the present inventor, failed to find a single transmission in which cam followers are the basis.